Iridium alloy for spark plug electrodes

Abstract

A spark plug comprises a shell having a substantially cylindrical threaded portion for threadable engagement in a cylinder head of an internal combustion engine, an insulator disposed coaxially in the shell, a center electrode disposed coaxially in the insulator, a side ground electrode having a first end coupled to the shell and a second end facing an end of the center electrode to define a spark discharge gap therebetween, and an electrode tip portion secured to either the side ground electrode or the center electrode proximate the spark discharge gap. The tip portion is formed from an alloy comprising from about 60 to about 70 percent by weight iridium, from about 30 to about 35 percent by weight rhodium, from 0 to about 10 percent by weight nickel, from about 3500 to about 4500 parts per million tantalum, and from about 100 to about 200 parts per million zirconium.

1. A wear-resistant electrode tip portion for securing to a spark plug electrode, the tip portion consisting essentially of:
 from about 60 to about 70 percent by weight iridium; 
 from about 30 to about 35 percent by weight rhodium; 
 from 0 to about 10 percent by weight nickel; and 
 from about 50 to about 100 parts per million cerium. 
 
     
     
       2. The tip portion of  claim 1 , wherein the tip portion is rivet-shaped. 
     
     
       3. The tip portion of  claim 1 , wherein the tip portion is substantially spherical. 
     
     
       4. A spark plug, comprising:
 a center electrode having a first electrode tip portion comprising an alloy consisting essentially of from about 60 to about 70 percent by weight iridium, from about 30 to about 35 percent by weight rhodium, from 0 to about 10 percent by weight nickel, from about 3500 to about 4500 parts per million tantalum, and from about 100 to about 200 parts per million zirconium; and 
 a side ground electrode having a second electrode tip portion comprising an alloy consisting essentially of from about 60 to about 70 percent by weight iridium; from about 30 to about 35 percent by weight rhodium; from 0 to about 10 percent by weight nickel; from about 3500 to about 4500 parts per million tantalum; and from about 100 to about 200 parts per million zirconium welded thereto. 
 
     
     
       5. A method for constructing an electrode for a spark plug, the method comprising:
 obtaining an electrode tip portion formed from an alloy consisting essentially of from about 60 to about 70 percent by weight iridium, from about 30 to about 35 percent by weight Rh, from 0 to about 10 percent by weight nickel, from about 3500 to about 4500 parts per million tantalum; and from about 100 to about 200 parts per million zirconium; 
 placing the tip portion in a welding fixture; 
 aligning the tip portion with the electrode; and 
 welding the tip portion to the electrode. 
 
     
     
       6. A method for constructing an electrode for a spark plug, the method comprising:
 obtaining an electrode tip portion formed from an alloy consisting essentially of from about 60 to about 70 percent by weight iridium, from about 30 to about 35 percent by weight Rh, from 0 to about 10 percent by weight nickel, from about 50 to about 100 parts per million cerium; 
 placing the tip portion in a welding fixture; 
 aligning the tip portion with the electrode; and 
 welding the tip portion to the electrode. 
 
     
     
       7. The method of  claim 5 , wherein the tip portion is formed by cutting a wire made of the alloy to a predetermined length, and forming the length of wire into a rivet. 
     
     
       8. The method of  claim 5 , wherein welding the tip portion to the electrode is by electric resistance welding effected by placing the electrode and the tip portion in upper and lower welding heads respectively, bringing the tip portion and the electrode into engagement with one another, and causing an electrical current of predetermined amperage to flow through the electrode and the tip portion while the tip portion and the electrode are held in contact with one another. 
     
     
       9. The method of  claim 7 , wherein welding the tip portion to the electrode includes forcing the electrode and the tip portion against each other with a predetermined force while causing the current to flow through both the tip portion and the electrode.